Imported copy of the ArrayStack class from
Commons Collections, which was the only direct dependency from Digester.

WARNNG - This class is public solely to allow it to be
used from subpackages of org.apache.commons.digester.
It should not be considered part of the public API of Commons Digester.
If you want to use such a class yourself, you should use the one from
Commons Collections directly.

An implementation of the Stack API that is based on an
ArrayList instead of a Vector, so it is not
synchronized to protect against multi-threaded access. The implementation
is therefore operates faster in environments where you do not need to
worry about multiple thread contention.